1. Field of the Invention
The present invention relates to a preparation method of 3-Nitro-1,2,4-triazol-5-one (hereinafter, referred to as xe2x80x9cNTOxe2x80x9d) from 1,2,4-triazol-5-one (hereinafter, referred to as xe2x80x9cTOxe2x80x9d).
2. Description of the Background Art
Research into NTO to apply as an insensitive high explosives had been confidentially performed in early 1980s in France. A result of research that NTO was applied to explosives was disclosed in U.S. Pat. No. 4,733,610 in 1987 by Lee et al. in Los Alamos national institute (USA). Since then, researches for applying to the insensitive explosives have been performed.
There are many processes for synthesizing NTO. Among them, the most generalized method is a two-step reaction which undergoes reactions as shown in below schemes 1 and 2, and in which semicarbazide. HCl is used as a starting material. 
There have been known many processes for preparing NTO from the TO as follows:
(1) The process suggested by Lee et al. in the U.S. Pat. No. 4,733,610 is as follows. TO is added to 70% nitric acid, and then the mixture was heated to the temperature of 55xc2x0 C.-60xc2x0 C. where a exothermic reaction is started. The reactor is then allowed to self heated until the reaction is complete. However, in this process, yield is only 65% based on TO, and it is disadvantages in that it is impossible to ensure safety because the temperature can not be controlled.
(2) Collignon et al. discloses a process which improves the problems of the U.S. Pat. No. 4,733,610 in US Statutory Invention Registration No. H861 (Dec. 4, 1990). In this process, temperature of 70% nitric acid is maintained at 65xc2x0 C.-70xc2x0 C., dried TO is added gradually into the nitric acid, and then the temperature is maintained until the reaction is completed. This reference describes that it takes 2-3 hours for this process, and the yield is 90% based on TO. In addition, they also suggested a successive process in which the supply of TO and 70% nitric acid to a reactor where the temperature is maintained at 65xc2x0 C.-70xc2x0 C. at a predetermined rate is carried out simultaneously with discharge at a same speed, and reported that the yield was 83% based on TO. However, since this process is performed at a high temperature, there are problems in that a rapid exothermic reaction occurs in the crystallization step of NTO, and subsequently, the problem of frothing of the reaction mixture is encountered. Especially, in UK Laid-open Patent Publication No. 2218986, it has been reported that the use of solid TO can lead to the formation of xe2x80x9chot spotsxe2x80x9d at the solid-liquid interface, and to a reduced yield of the desired NTO.
(3) European Patent application No. 210811 discloses a process to solve the problems of the above described exothermic reaction and foaming. In this process, 98% nitric acid and TO are mixed at a low temperature of 5xc2x0 C.-10xc2x0 C., followed by a three hour holding period at ambient temperature, followed by quenching with water at 0xc2x0 C. holding for 12 hours. However, this process is clearly very much time consuming. In addition, 98% nitric acid is relatively expensive starting material.
In the nitration process, the reaction rate is generally increased as the reaction temperature is higher, and therefore, the processing time is shortened. Accordingly, the conventional methods mainly use a high temperature process.
In case of NTO synthesis, it has been known that the highest yield is also achieved at the temperature range of 60xc2x0 C.-70xc2x0 C. However, in the process for preparing NTO, the initially generated NTO is dissolved in the reaction medium, and then the crystal is deposited at one time when the reaction medium is over-saturated as the reaction is proceeded. The amount of heat generated in a reactor is increased in a moment due to the heat generated during crystallization, and a large amount of foams are generated at the same time. Although such rapid exothermic reaction can be controlled with an automated cooling device, it is more desirable that a stable process is provided.
Therefore, an object of the present invention is to provide a preparation method of NTO with stability and high yield by solving problems of conventional methods such as a large exotherm and associated frothing during crystallization.
The object of the present invention will become more apparent from the following detailed description of the present invention when taken in conjunction with the accompanying drawings.